Piston pump improvement



Aug. 2, 1966 H. A. ALEXANDERSON ETAL 3,263,623

PISTON PUMP IMPROVEMENT Filed March 16, 1964 INVENTOR. HON 6E0 x9.ALEXANDERSO/V THEEO Q E. CHAMBERLAIN l) TTOENEY United States Patent3,263,623 PISTON PUMP IMPROVEMENT Howard A. Alexanderson and Theron R.Chamberlain, Utica, N.Y., assignors to The Bendix Corporation, Utica, N.Y., a corporation of Delaware Filed Mar. 16, 1964, Ser. No. 351,921Claims. (Cl. 103-162) The present invention relates to fluid pumps andmore particularly to an improvement in piston pumps of the wobble orswash plate type operating in extreme temperature, speed, or pressureconditions.

In prior art pumps of the wobble or swash plate type it is the normalpractice to provide relative rotation between a member containingreciprocating pistons and a tiltable wobble plate member. Intermediatethe pistons and wob ble plate, bearing shoes or slippers are interposedto permit changing angularity between piston and swash plate and toprovide a bearing surface with the swash plate. These bearing or shoemembers must accept the piston back pressure reaction force,frictionally slide at high pumping speeds against the swash plate, andbe exposed to whatever pump or fluid temperatures that are applied. As aresult the shoes or slippers deteriorate rapidly in service.

It is an object of the present invention therefore to provide a pistonpump construction designed to materially increase the life of shoe orslipper member from. that obtained heretofore-particularly under extremeoperating conditions.

Other objects and advantages of the present invention will becomeapparent from the following detailed description taken in connectionwith the appended drawings in which:

FIGURE 1 is a cross section view of a piston pump and wobble platemember illustrating a preferred embodiment of our invention;

FIGURE 2 is an enlarged cross sectional view of the pump piston andslipper member of FIGURE 1; and,

FIGURE 3 is a plane View of the shoe or slipper hearing surface of thetype illustrated in either of the prior figures.

Referring now to the drawings the portion of the piston pump illustratedin FIGURE 1 is comprised of a rotor which contains a tubular bore 12having a spline connection 14 adapted to be connected to a suitablerotary drive shaft, not shown. The rotor 10 is provided with a pluralityof angularly disposed cylinders 16 in which are reciprocably mountedplungers or piston members 18. The pistons or plunger members 18 have agenerally spherical or rounded end 20 over which is received a shoe orslipper member 22 which in turn bear against in sliding contact withrotatively fixed but tiltable wobble plate member 24, pivot trunnionsfor wobble plate not illustrated. Shoe member 22 is fabricated from adense metal material having high structural strength such as steel,bronze or alloys thereof. A cam plate 26 having'a central dependingflange 28 disposed within the central opening of wobble plate 24 isprovided with a plurality of openings 30 each of which is adapted toreceive a piston shoe 22. Cam plate 26 is urged into engagement withwobble plate 24 by means of spring 32 acting through a thrust member 34which is slidably mounted on an extension of rotor 10. Cam plate 26 isprovided to insure retraction of pistons 18.

In operation, drive means connected to spline connection 14 of rotor 10rotationally drives the rotor which carries with it pistons 18 and shoes22. As the shoes 22 rotate in a circular path they are urged against theface of wobble plate 24 by spring 32, thrust member 34 and cam plate 26.Thus the shoes follow the inclined surface of wobble plate 24reciprocating pistons 18 in cylinders 16 to create pumping action.

As pistons 18 move to the right on the pumping compression stroke fluidis raised in pressure and delivered to a receiving device. The fluidpressure additionally reacts on piston 18 producing a reaction force onshoes 22 creating a high wear condition between the contacting surfacesof shoe 22 and wobble plate 24.

It is known in the prior art to alleviate this fluid pressure reactionforce to a high degree by supplying fluid from the pumping chamber tothe bearing face of the shoe to aid in neutralizing or balancing thisreaction force. Such pump arrangements may be referred to as fluidbalanced piston pumps and it is our object to advance still further theextreme temperature, speed, and pressure conditions in which pumps ofthe fluid balanced piston tyfpe may be used while providing the maximumservice li e.

Referring to FIGURES 2 and 3 the piston 18 is provided with an axialfluid passage 36 extending fully through the piston and spherical end20. A similar fluid passage 38 is provided in the center of shoe 22 sothat fluid may pass from the pumping cylinder to bearing face of shoe.The extreme left end of spherical end 20 is ground flat at 40 to insurefluid connection between passages 36 and 38 when piston 18 and shoe 22are moved angularly relative to each other. A balancing recess 42 isprovided in the center of shoe 22 extending inwardly from the bearingface to form a pocket or reservoir for pump fluid and thus define anarea on which high pressure fluid reacts back on the combined shoe andpiston assembly to balance the fluid pressure forces. Immediatelyradially outwardly of recess 42 there is formed an inner circular rim orprojection 44. At the outermost radial extremity of shoe 22 an outercircular rim or projection 46 is formed such that rims 44 and 46 incombination form an annular recess 48. Each of the projections 44 and 46are of a dense metal having high strength. In the recess 48 there isdeposited an annular ring of soft bearing metal material having goodresistance to seizure or scoring such as silver, tin, cadmium or thelike.

While the bearing properties of silver, tin and cadmium are generallyknown in the art, what has not been previously recognized to ourknowledge is that these materials when applied to a balanced type shoesuch as that disclosed as by plating or the like and the pump issubjected to very sudden changes in pressure these metals will quicklydeteriorate at the edges.

We have found that providing a thin rim of dense metal around the innerandouter edges of the soft bearing metal that under the same severepressure changes the bearing metal does not tend to chip away or spall.

We believe that the bearing metals, which have a greater porosity,cannot withstand the very rapid changes from high to low pressures whichare experienced under severe operating conditions. The high pressure istrapped in the pores of the material and when the pressure is suddenlyreleased, particles of bearing metal are torn from the surface by theescape of the high internal pressure in the pores of the material. Byproviding rims 44 and 46 of dense metal such as steel or the like, whichare more homogeneous without the attendant porosity, in the criticalareas at the edge of shoe and balancing recess, this effect iseliminated. A further advantage is that the rim of dense metalcaptivates the bearing material and resists tearing from the shoesurface.

Although a particular embodiment of our invention has been described, itwill be understood by those skilled in the art that objects of theinvention may be attained by the use of constructions different incertain respects from that disclosed without departing from theunderlying principles of the invention. It is well known in the art towhich the .present invention relates that piston pumps may be run in thereverse direction to act as fluid motors without the exercise ofinvention.

We claim:

1. A piston pump comprising: a member having a plurality of annularlyarranged piston cylinders, a plurality of pistons mounted in each ofsaid piston cylinders, each of said pistons having a cylindrical portionextending slidably within said piston cylinders and a generallyspherical end extending externally of said cylinders, a tiltable wobbleplate member, a plurality of steel shoe members one for each of saidpistons having a bearing surface in slida'ble contact with said wobbleplate and a socket end fitted over said spherical end of said pistons,said shoes each having an axially centered recess extending inwardlyfrom said bearing surface, each of said plurality of pistons having afirst axial fluid passage, each of said shoes having a second fluidpassage fluidly connecting said recess and said first fluid passage totransmit fluid from said piston cylinders to said recess, each of saidshoes having an inner circular and outer circular projection of densemetal on said bearing surface formed adjacent said axially-centeredrecess and outer radial edge of said shoes respectively to form anannular recess therebetween; an annular ring of relatively porousbearing metal disposed in said annular recess having an upper surfaceflush with said inner and outer circular projections to provide a smoothbearing surface.

2. A piston pump comprising: a member having at least one off-centergenerally axially disposed piston cylinder, a cylindrical piston memberslidably mounted in said piston cylinder having one end projectingexternally of said cylinder, a tiltable Wobble plate member spaced fromsaid one end of said piston member, a shoe member intermediate saidwobble plate and said piston having an articulated connection with saidone end of said piston member and a bearing surface in slidable contactwith said wobble plate member, said shoe having an axially-centeredrecess extending inwardly from said bearing surface, passage meansextending through said piston member and said shoe member and throughsaid articulated connection to fluidly interconnect said axiallycenteredrecess and said piston cylinder, said shoe having an inner circularprojection of dense metal extending axially outwardly on said bearingsurface adjacent the radial outermost edge of said axially-centeredrecess, said shoe having an outer circular projection of dense meta]extending axially outwardly on said bearing surface at the radialoutermost edge of said shoe, said inner and outer circular projectionscooperatively forming an annular recess therebetween, an annular ring ofrelatively porous bearing metal disposed in said annular recess having asurface fiush with said inner and outer projections to provide a smoothbearing surface.

3. A piston and shoe assembly for use in a wobble plate piston pumphaving a wobble plate and a member having cylindrical piston cylinders,said piston and shoe assembly comprising: a piston member having acylindrica-l body portion and a generally spherical end, an axialthrough passage formed in said piston member ex tending through saidgenerally spherical end, a dense metal shoe member having a bearingsurface on one side and a socket connection on another side, said socketconnection fitted over said spherical end to provide an articulatedconnection between said shoes and said piston, said spherical end havingflat surface section providing a fluid chamber within said articulatedconnection fluidly connected to said axial through passage, said shoemember having an axially-centered recess extending inwardly from saidbearing surface, a fluid passage formed in said shoe memberinterconnecting said axially-centered recess and said fluid chamber withsaid articulated connection, said shoe having an inner circularprojection of dense metal extending axially outwardly on said bearingsurface adjacent the edge of said axially-centered recess, said shoehaving an outer circular projection of dense metal extending axiallyoutwardly on said bearing surface at the radial outermost edge of saidshoe, said inner and outer circular projections cooperatively forming anannular recess therebetween, an annular ring of relatively soft bearingmetal disposed in said annular recess having a surface flush with saidinner and outer projections to provide a smooth bearing surface.

4. A piston and shoe assembly for use in a wobble plate piston pumphaving a wobble plate and a member with piston cylinders, said pistonand shoe assembly comprising: a piston member having an axially disposedthrough passage formed therein, a dense metal shoe member having anannular bearing surface and an axiallycentered recess formed in saidbearing surface, an articulated connection interconnecting said shoemember with one end of said piston member, passagemeans formed in saidshoe member fluidly interconnecting said axiallycentered recess and saidaxially disposed through passage, said annular bearing surface comprisedprimarily of bearing metal, said annular bearing surface having densemetal retaining projections extending to said bearing surface at theedges of said bearing metal.

5. A piston and shoe assembly comprising: a piston member of generallycylindrical shape having an axially disposed through passage formedtherein, a dense metal shoe member connected to one end of said pistonmember and having a bearing surface formed thereon, a recess formed insaid bearing surface having passage means interconnecting said recessand said through passage, said bearing surface comprised primarily ofbearing metal deposited on said dense metal shoe member, dense metalprojections extending from said shoe member to said bearing surface atthe edges of said bearing metal to entrap said bearing metal.

References Cited by the Examiner UNITED STATES PATENTS 2,735,407 2/1956Born 103-462 3,075,472 1/1963 Garnier 103-162 FOREIGN PATENTS 1,161,7621/ 1964 Germany.

913,549 12/ 1962 Great Britain.

MARK M. NEWMAN, Primary Examiner. SAMUEL LEVINE, Examiner.

R. M. VARGO, Assistant Examiner.

1. A PISTON PUMP COMPRISING: A MEMBER HAVING A PLURALITY OF ANNULARLYARRNGED PISTON CYLINDER, A PLURALITY OF PISTON MOUNTED IN EACH OF SAIDPISTON CYLINDERS, EACH OF SAID PISTON HAVING A CYLINDRICAL PORTIONEXTENDING SLIDABLY WITHIN SAID PISTON CYLINDERS AND A GENERALLYSPHERICAL END EXTENDING EXTERNALLY OF SAID CYLINDERS, A TILTABLE WOBBLEPLATE MEMBER, A PLURALITY OF STEEL SHOE MEMBERS ONE FOR EACH OF SAIDPISTONS HAVING A BEARING SURFACE IN SLIDABLE CONTACT WITH SAID WOBBLEPLATE AND A SOCKET END FITTED OVER SAID SPHERICAL END OF SAID PISTONS,SAID SHOES EACH HAVING AN AXIALLY CENTERED RECESS EXTENDING INWARDLYFROM SAID BEARING SURFACE, EACH OF SAID PLURALITY OF PISTONS HAVING AFIRST AXIAL FLUID PASSAGE, EACH OF SAID SHOES HAVING A SECOND FLUIDPASSAGE FLUIDLY CONNECTING SAID RECESS AND SAID FIRST FLUID PASSAGE TOTRANSMIT FLUID FROM SAID PISTON CYLINDERS TO SAID RECESS, EACH OF SAIDSHOES HAVING AN INNER CIRCULAR AND OUTER CIRCULAR PROJECTION OF DENSEMETAL ON SAID BEARING SURFACE FORMED ADJACENT SAID AXIALLY-CENTEREDRECESS AND OUTER RADIAL EDGE OF SAID SHOES RESPECTIVELY TO FORM ANANNULAR RECESS THEREBETWEEN; AN ANNULAR RING OF RELATIVELY POROUSBEARING METAL DISPOSED IN SAID ANNULAR RECESS HAVING AN UPPER SURFACEFLUSH WITH SAID INNER AND OUTER CIRCULAR PROJECTIONS TO PROVIDE A SMOOTHBEARING SURFACE.